When aqueous reverse flow cooling is employed in an internal combustion engine, as disclosed in my co-pending application Ser. No. 907,392, it may be desirable to draw coolant directly from one of the engine coolant chambers into the pump and then subsequently force coolant by positive action of the pump to other engine cooling chambers or, alternately, directly to the radiator. Additionally, it may at times be desirable to select certain regions of the engine's cooling chambers for primary cooling, thereby assuring that those selected regions will always operate at a lower temperature than most other regions of the engine's head and block cooling chambers. This is important during critical cooling periods for the engine such as high ambient or high load conditions. Lastly, when employing the aqueous reverse flow cooling system described in my copending application Ser. No. 907,392, it is often desirable, in order to achieve maximum cooling efficiency when either constructing the pump to draw coolant directly from one of the engine cooling chambers or drawing first from the radiator and then passing the coolant to the cylinder head combustion chamber cooling area, to dedicate substantially all flow through only one coolant region of the cylinder head coolant chamber. With such dedicated coolant flow, there is little or no communication with other cooling chamber regions of the cylinder head or block coolant chambers until after substantially all the coolant has first flowed through the dedicated region.
If a coolant pump is configured to draw coolant directly from one of the coolant chambers of an engine as described in my co-pending application Ser. No. 907,392, a severe limitation is placed upon the maximum temperature level at which the coolant can be allowed to operate because some coolant vapor generated in the cylinder head cooling chamber during periods of high coolant heat and load will pass downwardly through the cylinder block cooling chamber by action of the pump's draw (vacuum) and enter into the impeller cavity area of the pump. Impeller cavitation substantially reduces pumping efficiency or, in some instances, may stop the pump completely. Even though the natural buoyancy of the coolant vapor causes most of the vapor to rise and be moved by the vapor circuitry, as disclosed in said co-pending application Ser. No. 907,392, some vapor will be inevitably drawn to the pump. This condition is aggravated when the pump is mounted directly to the cylinder block because of direct communication between the pump and the cylinder block coolant chamber. Additionally the greater the horizontal distance between the vapor take-off point of the cylinder head cooling chamber and the attachment point of the pump to the cylinder block cooling chamber, the greater the draw upon the vapor existing vertically above the pump attachment point and resulting in a greater amount of vapor being drawn into the pump.
When, in some instances, in order to facilitate ease of mounting and engine design, the pump drawside (pump vacuum) attachment point is moved towards to the cylinder head cooling chamber area whereby the pump will draw coolant directly from the head cooling chambers and subsequently force coolant to the cylinder block cooling chambers, the problem of drawing hot coolant vapor into the pump becomes more problematic during periods of higher coolant temperatures caused by high ambients and engine loads. The vacuum draw acting directly upon the coolant residing around the hotter combustion dome areas (spark plugs, exhaust valves, and runners in the cooling chamber will draw coolant vapor, as generated, directly into the impeller area and eye of the pump, reducing pump efficiency.
When employing aqueous reverse-flow cooling, as in my co-pending application Ser. No. 907,392, the use of a single cylinder head coolant chamber with multiple transfer ports to the cylinder block coolant chambers often causes a distribution imbalance whereby it is difficult to achieve an even flow volume distribution across the engine cross sectional area of the cooling chamber, especially in areas most distant from the coolant inlet. Also the use of a single cooling chamber for the cylinder head combustion chamber area of the engine does not allow for the design of the head cooling circuit to set a different coolant operating temperature level for one area of the cylinder head as opposed to a distinctly separate area but common to the same cooling chamber area, i.e., exhaust area versus intake area of the same cylinder head cooling chamber.